/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.format.datetime.standard;

import java.time.format.DateTimeFormatter;
import java.util.Locale;

import org.springframework.core.NamedThreadLocal;
import org.springframework.lang.Nullable;

/**
 * A holder for a thread-local user {@link DateTimeContext}.
 *
 * @author Juergen Hoeller
 * @see org.springframework.context.i18n.LocaleContextHolder
 * @since 4.0
 */
public final class DateTimeContextHolder {

    private static final ThreadLocal<DateTimeContext> dateTimeContextHolder =
            new NamedThreadLocal<>("DateTimeContext");


    /**
     * Reset the DateTimeContext for the current thread.
     */
    public static void resetDateTimeContext() {
        dateTimeContextHolder.remove();
    }

    /**
     * Associate the given DateTimeContext with the current thread.
     *
     * @param dateTimeContext the current DateTimeContext,
     *                        or {@code null} to reset the thread-bound context
     */
    public static void setDateTimeContext(@Nullable DateTimeContext dateTimeContext) {
        if (dateTimeContext == null) {
            resetDateTimeContext();
        } else {
            dateTimeContextHolder.set(dateTimeContext);
        }
    }

    /**
     * Return the DateTimeContext associated with the current thread, if any.
     *
     * @return the current DateTimeContext, or {@code null} if none
     */
    @Nullable
    public static DateTimeContext getDateTimeContext() {
        return dateTimeContextHolder.get();
    }


    /**
     * Obtain a DateTimeFormatter with user-specific settings applied to the given base Formatter.
     *
     * @param formatter the base formatter that establishes default formatting rules
     *                  (generally user independent)
     * @param locale    the current user locale (may be {@code null} if not known)
     * @return the user-specific DateTimeFormatter
     */
    public static DateTimeFormatter getFormatter(DateTimeFormatter formatter, @Nullable Locale locale) {
        DateTimeFormatter formatterToUse = (locale != null ? formatter.withLocale(locale) : formatter);
        DateTimeContext context = getDateTimeContext();
        return (context != null ? context.getFormatter(formatterToUse) : formatterToUse);
    }

}
